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A special simulation model for the surge responses of ZnO varistors is introduced in this paper. This model is based on the Voronoi network and contains the actual conduction mechanism of the grain boundaries, as well as the capacitances of the grain boundaries. The surge responses of the actual varistor samples were simulated and compared with the experimental results. The simulated waveforms agree...
The voltage gradient of ZnO based varistor is usually opposite to the average grain size. It has been reported that the growth of ZnO grains could be inhibited by doping with rare-earth oxides. In this paper the electrical properties and dielectric characteristics of ZnO based varistor ceramics with various Y2O3 additions are investigated. The voltage gradient of varistor samples markedly increase...
Rare-earth oxides can remarkably enhance the voltage gradient of ZnO varistors as growth inhibitor of ZnO grains. However, the effect of rare-earth oxides on the residual voltage properties of ZnO varistors has not been completely investigated. In this paper, ZnO varistor samples with various contents of Y2O3 dopant were prepared and tested under different currents of 8/20 mus impulse surge. When...
ZnO varistors have been widely used in power systems as metal oxide arresters (MOA) against overvoltage surges due to their excellent nonlinear current-voltage (I-V) characteristics and surge energy absorption capabilities. The MOA applied in power system with rated voltage usually has remarkable huge size, which results in great difficulty for MOA design and manufacture. Thus, ZnO varistors with...
The energy absorption capability is a key parameter for ZnO varistors. This paper discusses the nonuniformity of energy absorption capabilities of ZnO varistors. With experiment results, we show that energy absorption capabilities of ZnO varistors can be highly scattered, for different commercial varistors, and for the same varistors under diverse current waves. We explain this nonuniformity phenomenon...
A comprehensive review for the scattered phenomenon of energy absorption capabilities of ZnO varistors was presented in this paper. The pronounced and complex scattered phenomena were revealed according to experiments under varied test conditions. Those experiment phenomena were well explained by numerical simulations with microscopic circuit and heat transfer models of ZnO varistor based on Voronoi...
The influence of the geometry and topology of the granular microstructure, as well as the properties and the distribution of the different types of microjunctions on the features of bulk varistor devices is an important and interesting problem. Simulating analysis on the actual microstructure and electrical characteristics of ZnO varistors is used to effectively analyze the influences of different...
The U-I characteristics of ZnO nonlinear resistors (ZnO varistor) is very important on the protection performance of metal-oxide surge arresters, which protects power apparatus and electronic devices against surges. In this paper, the changes on U-I characteristics of ZnO nonlinear resistors are introduced when some rare-earth oxides are doped, as well as the mechanics which leads these changes. In...
ZnO varistors are vulnerable to be destroyed under high current. The puncturing phenomenon of ZnO varistor under high current is simulated in a microstructure model. The Voronoi diagram can effectively simulate the actual microstructure of ZnO varistors, from which the electrical topology relation of the nonlinear resistor network of ZnO varistor microstructure can be derived. The steepest descent...
Pore is an intrinsic property of ZnO varistor. There are two different shapes of pores in ZnO varistor samples, one is sphere shape, and another is irregular polyhedron. Pores are caused by air particles wrapped in initial varistor compact and grains-surrounded spaces during the sintering. By analyzing the pore phenomena in two different systems of ZnO varistors, we observed the pore ratio decreases,...
By comparing the experimental results of two different systems ZnO varistors, we identify that Sb2O3 is the origin of twinning in commercial ZnO varistors. The additive of Bi2O 3 weakens the effect of Sb2O3 to form twins while the Al2O3 dopant strengthens the twinning. The twins have obvious effect to inhibit ZnO grain growth and uniform its microstructure, because the formed twins result in increasing...
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